feat(ga): initial population generator with cognitive style coverage

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/unit/test_ga_initial.py

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+import random
+
+from multi_swarm.ga.initial import build_initial_population
+from multi_swarm.genome.hypothesis import ModelTier
+
+
+def test_initial_population_size():
+    pop = build_initial_population(k=20, model_tier=ModelTier.C, rng=random.Random(0))
+    assert len(pop) == 20
+
+
+def test_initial_population_unique_ids():
+    pop = build_initial_population(k=20, model_tier=ModelTier.C, rng=random.Random(0))
+    ids = {g.id for g in pop}
+    assert len(ids) == 20
+
+
+def test_initial_population_covers_all_styles():
+    pop = build_initial_population(k=12, model_tier=ModelTier.C, rng=random.Random(0))
+    styles = {g.cognitive_style for g in pop}
+    assert len(styles) == 6
+
+
+def test_initial_population_generation_zero():
+    pop = build_initial_population(k=20, model_tier=ModelTier.C, rng=random.Random(0))
+    assert all(g.generation == 0 for g in pop)
+    assert all(g.parent_ids == [] for g in pop)